Excessive Catalyst
by Ballerninja
Summary: John didn't know what to do. According to Sherlock, he was fine. There was nothing wrong. Of course there was nothing wrong. There was never anything wrong. Not with Sherlock Holmes. But when the famous detective has a mental breakdown in the middle of a crime scene, then something must be. Right?


A/N: So... New Story! Instead of posting a new chapter in _Switch the Patch_ , I've decided to post this. (Don't get too excited, Moriarty, but this is indeed to story I was telling you about. Good job finding it.)

Disclaimer: If you recognize it, I probably don't own it. Also, I'm American, and this is my first fanfic for this fandom. So go easy on me, because I tried. And it's late. Or... early. It's one in the morning. I'm going to sleep now.

* * *

"Stop it."

The flat had been silent. Peaceful as it always was when the famous Consulting Detective retreated into his mind palace for a refurbish. Or a cleaning. Or… sorting? What he actually did in there was a mystery to everyone except the man himself. And perhaps his brother. Mycroft Holmes, if you were to ask the man, knew everything, of course.

So when the two words drew John away from his computer screen, he was slightly startled. It had been hours, and Sherlock hadn't even twitched one of the long fingers gently pressed against each other as their tips rested lightly just under his nose since he'd first settled.

"Sorry?"

"Your typing, John." Sherlock snapped. "It's annoying."

Trying to resist the urge to snap back, John shifted in his seat, feeling his lower back ache from the position he'd been slouched in for the past hour. "I'm not going to stop doing something just because you tell me to, Sherlock. We share this flat. You're not the boss. I'm writing."

They'd had the same conversation millions of times, and so John had built up a rhythm. One he was used to. Sherlock would tell him to stop doing a thing. John would argue that Sherlock was not in charge, and the thing wasn't causing harm, nor was it purposely annoying. Sherlock would snap back some sort of insult to either John's intelligence or his family. Normally the former, unless Sherlock was having a particularly nasty day. Then he would let it go, either because John didn't mind stopping, or because it really wasn't that much of an issue in the first place, and Sherlock had just… felt the need to make himself known. Well, that was John's translation. He could never really tell why there were days the dark-haired man felt the need to nit-pick something of his flat-mate's actions.

This was why, when John's argument wasn't addressed at all, the army doctor was thrown off balance. The silence stretched for a while, and John simply stared at where Sherlock was crouched in his chair. The detective's curly hair was casting odd shadows on his sharp cheekbones, as the only light was one from a tiny lamp in the back corner, barely enough to see in the half-light of the evening. Sherlock hadn't moved again. Not to insult, at least. Maybe he had just gotten caught up in his memory technique again, and was pulled under before he felt the need to respond in any way.

And, of course, John had stopped typing on his computer.

Hesitant and curious, John typed out a few words without looking away from the Consulting Detective. At the fourth, Sherlock silently seemed to grimace and he shifted his weight as if he were suddenly uncomfortable. That was a puzzling reaction.

"Are you feeling all right?" John asked, the doctor in him wanting to kick in and throw diagnoses into the front of his mind before he even had a list of symptoms. He quickly pushed it down. It was the friend in him that was causing the anxious rush for answers. But if he'd learned anything about Sherlock it was that pushing for those answers was not the way to go about things.

So he waited. After a few moments of a thorough silence, John contemplated the idea that Sherlock hadn't even heard him. But then the genius spoke.

"I think I'm catching something. But I'm not bothered. My immune system is strong. I'm regularly healthy. Still young. The sickness will most likely die relatively soon." Was the reply. The honest reply.

Frowning slightly, John asked "When was the last time you ate?"

A standard question for Sherlock Holmes. There was a list. That was the first. Second was "What did you have to drink last and when?" followed up by "How much sleep have you gotten in the last forty-eight hours?" and normally one of these would tell you the exact problem and how to fix it. Sometimes more than one. Because Sherlock only did the bare minimum to keep functioning because his time could be better spent on some study or another, in his opinion.

Sherlock opened his eyes, and frowned in John's direction. "Honestly, John? I ate take out with you not three hours ago."

Had he really? Ah, yes. Asian from down the road. It had been delivered.

"When did you last have a drink?"

"Not this again. If it does manifest, it will probably just be a cold." Sherlock's voice was sharp, but John knew it was just Sherlock's reaction to his caring.

Sometimes it was as if he didn't know how to react at all. But John only ever contemplated this for a few seconds before going about his day. As he would now.

"So you have drank something, then?"

There was a deep sigh from the detective. "Yes. And before you ask, the answer is ten."

Ten? Oh, ten hours of sleep in the last forty eight. John sighed. That was the bare minimum he would allow before giving a nap order, and Sherlock knew it. Sadly, John didn't know if the other man was being honest with his numbers, or just saying it to get John off of his case. It could be either, he supposed.

The army doctor let it slide, this time. And Sherlock went back to his silent retreat to the depths of his memory, where he always seemed to be able to escape to. John had wished on occasion that he could also do such an advanced memory technique, but quickly dismissed his interest when he recalled the fact that he would be able to remember everything. Handy for being a doctor, but not for being a soldier. And, of course, he could delete the memory, as Sherlock had of things like the solar system, but that seemed… intrusive. Even though it was his own mind, the idea of deleting anything from it intentionally seemed wrong. As if it would strip him of his own identity. Because, in his mind, everything he'd experienced, even the bad, was crucial to the building of his personality.

So John quickly dismissed his interest, but not his fascination; that Sherlock was able to organize his mind in such a way was amazing. Awe inspiring. Not that he would tell Sherlock that. The man already had an inflated ego as it was. And while encouragement was good, praise was not. And there was a difference. Most people couldn't tell it, though. The only evidence was in the impact.

John sighed deeply, without realizing it, as he rubbed the inner corners of his eyes before glancing at the time. It was nearly eleven at night. Time for bed then. He had work tomorrow.

As he closed his laptop and made his way to standing, he looked once more at Sherlock. "I'm knackered. See you tomorrow." John waited his customary three seconds for a reply before heading up the stairs, his mind temporarily going to his friend's aggravatingly odd sleep cycle before returning to thoughts of his own.

* * *

Sherlock attempted to resist the mostly overwhelming urge to roll his eyes. And failed. It seemed his control was lacking as of late. Not that he was really trying that hard. Anderson was a complete idiot, and the Consulting Detective could only deal with so much of that on a regular day. Not when he was fighting some sort of virus. He'd told John it was nothing, and it would be. He just needed to get past the initial bit, and he would be back to normal.

Back to being able to handle ignorance.

At least to a greater extent than he seemed capable of currently.

As Sherlock was crouched next to the body, trying to gather evidence, he realized something abruptly; he couldn't focus. Not on the blood spatter, which indicated that this was only the dump site; it was a line of drops in the shape of childish suns as it fanned out, suggesting the body was carried, and only shortly after the death. There had still been a steady trickle when it had been disposed of in the alley. Sherlock understood this, and processed it. But he couldn't focus on it or what it could mean for the case.

He couldn't focus on the dirt packed into the soles of the victim's boots, with pieces of mulch sticking out, only one of the many signs indicating landscaping. And his mind catalogued, but quickly passed over, the foot prints he had seen upon entering the alleyway that hadn't belonged to a landscape artist; business shoes. High priced, he would know and remember if the smell of rot wasn't so strong, and if Anderson would just _stop talking_.

Sherlock stood just milliseconds after his realization as he tried to regain control of himself. Every grain of dust on the jacket of the victim stood out. Just as the fibers in Sherlock's own coat as he caught a glance at the dark sleeve when he lifted his hand to curl his fingers into his hair.

The first steps of decomposition had settled in, but Sherlock was familiar and comfortable around all of the stages of death, so it wasn't that. Was it the garbage itself, the stench of the rotting rubbish, ripping a hole through his brain? And the high, nasal voice that would _not_ shut up. Talking of different theories about how perhaps the victim had walked there, or maybe this had been the scene of the murder because there was so much blood. All ludicrous, and if the buffoon would simply look, instead of attempting to insist Sherlock was wrong, he would realize that.

But the voice continued. And there was Lestrade's deep voice, and John's whispered reply, and Donovan's from further into the alley, and the scuff of boots on pavement, and the shift of plastic against itself. Noise. Heavy static on a radio. Muffling. Deafeningly loud. Lights. Bright. From the road. The torch in Lestrade's waving hand. Flash, from cameras for evidence. Blinding. Feelings. Plastic gloves. Hard magnifying glass. Socks tight around his ankles. Hair in his hand. Scarf around his neck. Suffocating. Too loud. Too bright. Too loud. Too… too much.

The world was going in and out of focus. Was there an earthquake? Why was his hair shaking? That's impossible. There's no motor capability in hair. What was shaking? Trembling? Was… was it _him_?

It felt like an overdose. A minor one. Not life threatening. But he hadn't touched a needle in months. And it had been weeks since he'd smoked at all. But it felt familiar. Painfully familiar. His eyes refused all commands to focus on anything. Even when something loomed close to his face, he couldn't get them to cooperate, the traitors. And he was feeling light-headed. Quickly, he dug through his mind palace, desperate for an answer to what was happening, when suddenly it hit him like a train. So quickly it hurt. He winced, and physically as well as mentally stepped backward, only to nearly trip over his own feet. A set of hands caught him, sending numbing needles into the area of contact. Catching him before he fell to the ground completely, but like an electric shock in a pool. Agonizing.

He tore himself away from the grip, feeling the desperate need to get away, and ran into something else. What was happening to him? He was normally so aware. And then his previous realization was brought back forward in his mind to be reanalyzed. It wasn't that he couldn't focus on _anything_ , it was that he was focusing on _everything_.

The overwhelming noises, lights, sights; he knew he recognized this feeling. And he did. It was horrible. No. Facts. Focus on facts.

Enhanced senses; overpowering. He couldn't control what he was taking in or discarding. But what was causing it? A memory pried its way through his muddled emotions to help him recall a moment from his earlier years. When he'd begun deducing in his regular life. The reason he turned to drugs; not for enhancement, as everyone thought. Not normally. Not for regular days. No… it was the numbing sensation. The withdrawing-from-reality was his favorite part. The part he needed.

He was over stimulated.

"—lock, you're really beginning to worry me now." John's voice pierced his thoughts, as it always seemed to on the worst of days. The Consulting Detective had to resist thanking the doctor profusely for helping him regain focus as he turned his attention completely to the familiarity of his flat-mate.

"Ah, you're back." John did seem worried. But his voice didn't betray him; it was his eyes. Lightning fast, scraping and analyzing every part of Sherlock's appearance, not unlike deducing. "So, what was that just now? Do I… Do I _need_ to be worried?"

Sherlock realized with a jolt that he was, in fact, leaning against the wall of the alley, mostly slouched inward on himself in a nearly defensive position. And his breathing was heavy. As if he'd just sprinted miles. Wait… lightheadedness? He'd been hyperventilating. No wonder John looked worried. The genius looked around to see what his apparent breakdown had done to the officers and felt oddly surprised at what he saw.

They were all pointedly looking away from him and John. They were all making a conscious effort to avoid even glancing in his general direction. Every. Single. Officer. He vaguely wondered why. Then he recalled John. His eyes drifted back to the army doctor to see a growing expression of concern forming on his face. Almost concern. More… worried. There'd been a lot of that lately.

"Should I call an ambulance?"

"N-no." Sherlock was horrified by the stutter, but pressed forward in an effort to ignore it. "No, I'm fine. It's… a thing."

John, looking slightly relieved at the sound of his friend's voice, lifted an eyebrow. "A thing? As eloquent as ever, Sherlock."

The detective glared slightly, before straightening himself and righting his coat. "I'll explain later. First, let's tell Lestrade about his killer."

* * *

John didn't know what to do. According to Sherlock, he was fine. There was nothing wrong. Of course there was nothing wrong. There was never anything wrong. Not with Sherlock Holmes. But when the famous detective has a mental breakdown in the middle of a crime scene, then something must be. Right? It couldn't be nothing if there was something. Now he was thinking himself in circles.

Apparently the murder was an easy one. One that "even Anderson could figure out. No, never mind, Anderson's an idiot. But you could, Gavin."

And the reply was "It's Greg. And is that it? No… helpful advice?"

There was no follow up. Sherlock just stalked away as if nothing had ever occurred. And, with a quick apology for the detective – he always seemed to be apologizing for him – John chased after him. And into a cab they went. John waited again. He seemed to be doing a lot of that as well. Waiting. For Sherlock Holmes. In the odd silence of the cab, which was normally rather pleasant, John waited. Because he wouldn't push. Sherlock was a functioning, responsible adult who—no, not really responsible, but he was a functioning adult. Or, well… he was an adult. Unless he was acting like a two-year-old. Which he was most of the time, in John's opinion. A genius two-year-old.

Legally, to everyone but a certain Holmes in the government, Sherlock was an adult. Therefore, he could function on his own, without help. And it's not like John had been there for the other man's entire life, and Sherlock was still alive when he got there. So that meant, of course, that Sherlock could take care of himself. It was the only logical conclusion, as his friend would say.

Then he couldn't wait. "Seriously though, what was that?"

"Wow, John, an entire twelve seconds. I'm impressed." The dry humor in the reply had not been what John had been expecting. Blatant avoiding of the subject was more accurate.

"You said you would explain."

"Later. I said later."

That was more like it. "How much later is later, Sherlock? Because that's not a logical way to measure time."

"Listen to you, talking of logic as if you understand it." Sherlock's tone was condescending. Something John was used to. And hated. It made him feel inferior. And, well, just because he was didn't mean he wanted to be reminded of that.

So the army doctor took a deep breath. But just as he was going to respond, Sherlock cut him off.

"It was nothing." He said.

John narrowed his eyes. "No, that wasn't nothing." Sherlock didn't answer, so John pushed forward, against his better judgement. "You practically collapsing at a crime scene isn't nothing. I should have called an ambulance."

"I'm fine. It isn't a physical problem." That wasn't as reassuring as Sherlock had hoped it to be.

Then a realization struck, and John's eyes widened. "Have you—"

"No."

"You didn't even let me—"

"I'm not on anything." Sherlock snapped before looking sullenly out of the fogging window. "I've been clean for months."

The silence stretched in the car.

"Okay. All right. So, it's a mental issue, and it's giving you trouble. Enough that you're temporarily unresponsive in the middle of crime scenes. That… that isn't good." John said. "What's happened?"

"Nothing."

"Do you think I'm blind?"

"Sometimes."

"Sherlock, this isn't funny."

"No, you're right. It's not." Sherlock agreed. "Now can we drop it?"

"No."

"Why _not_?" the detective practically shouted, twisting in his seat to look at John directly.

"Because I care about whether or not this is something that will harm you." was John's cool reply.

Sherlock melted into his seat and put a hand underneath his curls to lay over his eyes. There was no more conversation the rest of the ride. When they got to 221B, John paid the cabby, and apologized for their argument with an extra tip.

The Consulting Detective and Army Doctor went in through the door. Upon entering, Sherlock shed his coat and placed it on its normal hook. Or… tried. It missed by a millimeter and fell to the ground in a lump. Sherlock stood, arm still outstretched as he stared at where it had fallen.

John frowned as he slid off his own jacket and hung it on a different hook. The detective frowned deeply, the furrowing of his brow an unusual look, and it took John a moment to understand why; the expression was formed in confusion.

Equally baffled, John decided to take pity on his friend and he grabbed the infamous coat himself and lifted it off of the ground. He hung it on its rightful place, and looked again at Sherlock. Now the detective was looking at his fingers, where they were still stretched out toward where his coat now hung.

"Sherlock? Are you alright?" John asked.

The dark-haired man shook his head as if to dispel a cloud before passing John to take the steps. The shorter of the two loyally followed.

When John entered the flat itself, he found Sherlock pacing, rubbing the back of his head. He looked somewhere between panicked, nervous, and disappointed. It was such a bizarre combination that John could do nothing but stare as the genius puzzled through something or other. Had this something to do with him dropping his coat? In fact, Sherlock was still wearing his scarf. He hadn't taken it off. That was odd in itself. Perhaps the change of situation was messing with him. A creature of habit had never been how John had pictured Sherlock, but the more he thought about it, the more it made sense.

Before the thought could go much further, there was a frustrated growl from the detective as he stopped and fiercely ruffled his hair before throwing himself onto the sofa, his breathing rough as if he'd just been running. That was a bit disconcerting.

But John didn't ask what was on his mind. He didn't want Sherlock to hide himself in his room, or something of the like, because John had asked him the same question too many times. He could hear the words of response as clear as day; _You're sounding like a broken record. The need to repeat a question so many times only exists in science experiments._ So John didn't ask. He just made himself comfortable on his chair, and entertained himself by looking out the window and watching the birds nest on the top of the building across the street.

The movement of Sherlock launching to a sitting position on the couch drew John's eye. He watched as the consulting detective ripped off his scarf and lobbed it at the table against the wall, sending the already precariously piled papers gliding in a ginormous mess onto the floor.

John stood. " _Sherlock_!" He scolded.

Only halfway to picking up the mess did he realize there had been no further movement from the detective. He was still sitting on the sofa. His long, pale fingers interlaced with his hair, creating a sharp contrast between the dark curls and the ivory skin. Through his normal purple shirt, John could see his hunched shoulders as they tensed. His breathing was slow. Deliberate. It was as if keeping control of it was the only thing keeping him alive, so every breath was measured meticulously. Until there was a quaver. The tiniest shake, and a sharp exhale. The fingers curled tightly into fists, no doubt pulling hair with it.

Forgetting entirely about the papers, John carefully approached and sat next to his friend on the furniture. From this angle, John could see that Sherlock's lips had been tightened into a thin line, and he was breathing harshly through his nose.

"You know how to breathe, Sherlock." John said quietly. "And you know you're not doing it effectively. Come on, sit up." He reached forward and nudged the front of the man's shoulder. Sherlock let his hands slip out from his hair as he straightened his spine, but he kept his head ducked so his dark hair still hung in front of his eyes from John's perspective.

Then John watched as Sherlock went through steps that a doctor would know well without any guidance. He straightened his spine, rolled his shoulders back to expand his chest, and finally lifted his head so that his airway wasn't restricted by his own muscle. He breathed in through his nose, then out through his mouth. Five counts in. Hold for one. Six counts out. Hold for one. Repeat. An effective, simple count, and one John had used himself when he'd wake up from particularly awful nightmares. But Sherlock wouldn't know that. He probably read about it in some article or another.

"What's going on?" John asked, his tone a mimic of his bedside voice that he used for patients.

Sherlock wouldn't meet his eyes, as if he were embarrassed by something. He waved his hand in the air, and John was surprised to see it tremble slightly. "I'm getting a cold."

John couldn't help his small bark of laugh. "I'm pretty sure nervous breakdowns aren't a symptom of the common cold."

"It is for me." He admitted. "Just… not normally. I have – had something to ease this part. These nervous breakdowns, as you called it. I just hadn't been expecting it this time. Normally I'm careful."

"Okay, I'll say it; you've lost me. What are we even talking about?"

Sherlock frowned thoughtfully, taking a few more breaths as he had before. "Imagine a funnel. You pour water into it, and so long as you carefully pour the water, it will stay in the funnel and come out the hole on the end without issue. Correct?" At John's flummoxed nod, he continued. "Now imagine someone taking an entire bucket of water and pouring it into this tiny funnel all at once. What would happen?"

"They'd spill the water, obviously." John answered. "It would pour out over the edge."

Sherlock nodded in affirmation. "There are two solutions to this problem; build higher walls or pour slower, yes? But higher walls only solve the problem temporarily, as you could still overflow if you aren't careful. So you just have to pour slower."

"What are you getting at?"

"The water is information, John. Outside stimuli. The funnel represents, in essence, the amount of it you can process as you take it in through your senses. Most people never have to worry about an overflow, as they only ever take in exactly the amount that would fit through their funnel. Those who do take in more have to either build up a tolerance to the level of stimulus, or regulate it as they take it in, disregarding the unimportant information for later, if they go back to it at all. And, with a lot of practice, some can take in everything, and process the overall image in individual pieces as the need arises."

Sherlock paused here, and John wondered if it was to catch his breath as he'd said that entire piece as quickly as he spouted his deductions. When he didn't continue, John decided to ask a question of his own. "So… if that entire bit with the funnel was a metaphor, then what is the real equivalent of an overflow?"

His flat-mate took another deep breath, and tipped his head to look at John nearly sideways. "Think about it for a moment."

Deciding not to roll his eyes, John did just that. He began to speak slowly, thinking aloud. "You said that the water was outside stimuli, right? Like… sounds, smells, all of that? Then… overflow would be too much of that. Right? Something… something of an overwhelming feeling?"

"The technical term is overstimulation." Sherlock confirmed. "And it is indeed someone taking in and processing too much of everything all at once."

"So, when you can't control your deduction thing?"

Sherlock snorted. "You make it sound like some sort of super power. But you're along the correct line. There's something else you need to understand, though. The bucket being poured in all at one time is relative to hypersensitivity. Massive amounts of stimuli thrown in the mix at once." He nodded, more to himself than John. "It's not something only I have. Others do as well. It's not common, but it's not rare, either." He admitted. "It actually helps."

"Helps with what?"

Sherlock grinned at his friend. "The deduction thing." He mimicked. "I'm automatically taking in all of the information. The problem most people have is associating all of those things with real-world facts. That part is where it becomes deductions."

John nodded to show his understanding before frowning. Just as he opened his mouth to ask his question, understanding cleared his face. "That's what happened at the crime scene."

Sherlock nodded. "That's exactly what happened. Though it didn't help that I opened myself up to it; I was prepared for regular deducing, and didn't account for the rest of the factors."

"Which are…?"

"My extra sensitivity when I'm sick." He said without pause. "It's the same when I'm deprived of sleep. That's why I take regular naps, you know. I'll always sleep the right amount to stay awake enough to prioritize information. You don't have to worry about that."

" _That_ is why your getting a cold was relevant to any of this?" John asked.

Sherlock nodded and looked back forward so that he was no longer looking at John. "Yes."

The doctor said nothing, instead followed the detective's gaze to the skull on the fireplace. The silence stayed for a while. Companionable. Not at all uncomfortable or awkward. Not that Sherlock would have noticed; John found that out rather quickly after he moved in. The man had no way of sensing what the populace called "awkward silence". It was almost amusing sometimes, and comforting in others; John never felt like he had to fill any lapse of silence when he was with his friend.

"When I was younger, these sort of… lapses used to be frequent." Because of where John's train of thought had traveled to, it took him a moment to understand that Sherlock was still talking about the over stimulation. "And I didn't know how to manage it. In my adolescence, I wanted nothing more than reprieve." Sherlock's voice was quiet. Not quite a whisper, but lower than his normal volume. It was secretive. Revealing. Almost vulnerable. It was a side John had never seen before, and indeed it wasn't something he was sure he wanted. Did he want Sherlock to open up more emotionally? Yes. It was only healthy. But… did John really want his perception of his friend to change? Because living with Sherlock Holmes was already chaos. Already so insanely disordered that the idea of any other large thing thrown at him was daunting.

"I'm sure you wondered. Everyone does." Sherlock said, even quieter than before.

John furrowed his brow. "What are you talking about?"

"Why would you risk it?" He said with a tone that was mocking. "Why would someone with a mind so vast in information, with so much potential, risk so much damage for a high?"

Oh. That's where this was going. John prepared himself mentally for the possibility of backlash from his friend as he listened intently to whatever Sherlock was going to say next. Who knew how much he would share before he stopped and locked himself away again?

"Well… now you know. A scared child that had the world attacking his mind, and no defense. That was who made the decision the first time. The promise of relief was what first hooked me, and the rest… is what happens to everyone. They get addicted." He took a steadying breath. "Well, I think that's enough drama for one night, don't you? I'll probably be bedridden by this time tomorrow, anyhow."

Sherlock abruptly stood and moved to his violin.

John blinked as his mind tried to catch up. "Wait, I thought you said you would be fine."

"And I will be. Upon further examination, I think I've caught the flu. I'm already feverish." He admitted as he tightened the hair of his bow. "I'll be sniffling by morning, and practically coughing up my lungs. Allow me to enjoy this peace while I have it, John." Sherlock lifted his instrument and began playing a simple melody John had heard often, but never asked the name of. He often suspected that it was composed by the detective.


End file.
